I think he was lazy, ignorant, and too reserved in recruiting until 2014, but I don't think he was necessarily a bad evaluator. BYU has had a bunch of lower end guys pan out. That shows he (and staff) actually does evaluate well a lot of the time.
For the guys who don't turn out, well, I think that's much less about poor evaluating and more just about lazy recruiting. For quite a while they were guilty of getting their top few guys and just settling for the low end leftovers in 2/3 or more of their recruiting. It was a lazy approach to find kids who were just a "good BYU fit" regardless of talent or potential.
The "limitations" BYU has in recruiting were intensified by Bronco. They were much more harsh than they should have been. Now that Martzen and others got him to open up, it's changing some. But they're still fairly decent at evaluating.